This mod for Far Cry 3 is called "Z-Day," and its creator says the name will be changed to something else before its final release is offered. It sort of shows how brand confusion can work in reverse, too, when people might confuse your game for something that it's really not, and you really don't want them to think that, either.
Modder GC Vos says "Z-DAY" is nothing like DayZ and these 7 minutes of gameplay (from back in November) would seem to bear that out. It's a set of 12 missions "much inspired by games like Left 4 Dead but with a Far Cry twist to them," he says.
Still, the name change is not an insignificant thing. "We've come to the conclusion it is indeed too similar to other titles, so we will be deciding on a new name very soon," GC Vos said in a comment underneath the YouTube video (above) announcing plans for an open beta on March. "This does come at the price of significant changes to already existing animations, pages and banners, so I hope you guys will grant us some time to come up with a good alternative."
So what's the point of the mod? Using the Far Cry engine, it introduces an element of stealth to a zombie FPS, though the pistol-packing approach also pays dividends. Unlike Left 4 Dead, you can hide and proceed a little more cautiously without having the Director spawn a bunch of infected to chase you off.
Far Cry Z-DAY mod is not just a DayZ clone [PC Gamer]